SUPERIOR FACE OF THE BODY. 117 



Its uses are of primary importance, because it receives the saddle 

 and the weight of the rider. It transmits to the anterior part of the 

 body the efforts of propulsion, which are communicated through the 

 loins by the posterior limbs. The back therefore fulfils, by its con- 

 formation, diverse requirements which we will describe. 



Direction. The back may present several directions. It is 

 straight when it describes almost a horizontal line from before to behind. 

 A straight back is a sign of great strength, for all the weight which the 

 region supports is borne by the bones and tends to efface the rachidian 

 arch. The saddle will, in this conformation, rest in a good position. 



The back is convex (or the animal is roach-backed) when it is slightly 

 arched, prominent, and sharp near the region of the loins. Such a con- 

 formation increases the conditions of solidity to external pressure, in 

 which the preceding form is deficient, on account of this arch being 

 exaggerated. It is incorrect to associate this condition with flat ribs 

 and a narrow chest. Convexity increases the reactions of the back and 

 shortens the gaits of the animal. The constituting vertebrae in this 

 disposition are related in such a manner that all pressure made upon 

 them from above to below is supported more by the bones than by the 

 ligaments which unite them, whence less elasticity and flexibility in 

 executing its various functions. The convex back, besides, is generally 

 shorter than the other forms, and does not permit sufficient freedom to 

 the extension and flexion of the posterior members in taking long and 

 rapid steps. It is therefore a centra-indication of rapid locomotion. 

 Horses in which it is observed are predisposed to forging; that is to say, 

 the fore and hind feet touch each other when their speed is increased. 



The convex back, for these reasons, is a defect in saddle- and driv- 

 ing-horses ; in those performing, on the contrary, slow and heavy 

 work, it is of no consequence. 



When the dorsal region is concave from before to behind, the 

 animal is designated as sway-backed or hollow-backed. This conforma- 

 tion, congenital or acquired, is more faulty than the preceding, and any 

 load borne upon it tends to efface the arch formed by the vertebrae of 

 this region. Instead of the latter offering a resistance, from their 

 mutual contact, to the weight which they support, such weight is almost 

 entirely sustained by the ligaments. This fact makes the vertebral 

 column become rectilinear or, when exaggerated, convex along its in- 

 ferior border. The ligaments which maintain the dorsal arch normally 

 are therefore submitted to constant traction during service, particularly 

 if a weight be superadded to that of the viscera. We have often 

 observed in old horses more or less voluminous exostoses disposed in a 



